Conventionally, there have been cases where a stent formed from metallic wire or the like in the shape of a hollow cylinder having a multiplicity of openings in its side wall and which is expandable in a lumen of a living body, such as blood vessel, bile duct, trachea, esophagus, urethra, etc., is used for improvement of a lesion part (stenosed part or obliterated part) in the lumen of the living body.
For instance, a stent having a self-expanding function (self-expandable stent) is delivered into a lumen of a living body while in a compressed state and contained in a gap between an inner tube and an outer tube, in a distal portion of a delivery catheter having the outer tube disposed over the periphery of the inner tube. Then, the outer tube is retracted proximally to release and expand the stent, whereby the stent can be put indwelling in the lesion part. In the stent delivery system having the stent and the catheter of this kind, there are cases where, for example, the outer tube and the inner tube are inserted into a winding lumen of a living body and are advanced into a lesion part. In this case, the space provided between the outer tube and the inner tube may cause bending and buckling of the outer tube.
In view of this, there has been known, as for example disclosed in JP-T-2002-525168 and JP-T-2006-525834, a stent delivery system wherein a coiled spring is provided between an outer tube and an inner tube so that the outer tube can be supported when the outer tube and the inner tube are bent in a lumen of a living body.
In the stent delivery system disclosed in JP-T-2002-525168 and JP-T-2006-525834, however, both ends of the coiled spring are connected (fixed) to the proximal end (base end) of the stent and the inner tube. When the inner tube and the outer tube are bent, therefore, the spring provided inside cannot follow up to the bending, so that stress concentration occurs at the contact point where the spring makes contact with the inner circumferential surface of the outer tube. As a result, the bent outer tube cannot be evenly supported by the spring. In addition, kinking (sharp bending) may take place, with the contact point between the bent outer tube and the spring as a starting point. In such a situation, the distal ends of the outer tube and the inner tube of the stent delivery system cannot be delivered into a desired portion in a lumen of a living body.